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Fungal. Virus. Sweet Corn Diseases. Common Rust - Puccinia sorghi Smut - Ustilago maydis Northern Corn Leaf Blight - Exserohilum turcicum (Helminthosporium turcicum). Maize Dwarf Mosaic. Maize Dwarf Mosaic Virus. Maize Dwarf Mosaic Virus. Aphid Vectors.

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Presentation Transcript
sweet corn diseases

Fungal

Virus

Sweet Corn Diseases
  • Common Rust -Puccinia sorghi
  • Smut - Ustilago maydis
  • Northern Corn Leaf Blight - Exserohilum turcicum (Helminthosporium turcicum)
  • Maize Dwarf Mosaic
slide5

Maize Dwarf Mosaic Virus - Key Points

  • Symptoms:
    • Mosaic pattern of light and dark green streaks along and between veins
    • Most striking in whorl stage
    • Evident on flag and husk leaves
    • Poor cob fill, stunted plants, reduced yield
    • Increased rust problems
  • Many strains of MDMV identified
    • Strain A: Source = Johnsongrass
    • Strain B: Johnsongrass is not host
  • Infects all types of corn and many grass species
  • Transmission: Aphid species
    • Corn leaf aphid is primary vector
    • Nonpersistent transmission
slide6

Maize Dwarf Mosaic Virus - Control Strategies

  • Resistant cultivars
  • Planting to avoid peak aphid flights
  • Eliminate perennial grass hosts
  • Insecticide sprays may control aphids but not transmission
slide10

Sweet Corn Rust - Key Points

  • Pathogen: Puccinia sorghi
  • Symptoms:
    • circular to oval, orange-brown pustules
    • on leaves husks, necks, tassels
  • Can overwinter in southern US as urediospores, these spores are wind-borne to new areas as corn is planted progressively northward
  • Infection favored by:
      • temperatures 59-68° F
      • about 24 hours of very high humidity or dew for germination and infection
  • Multiple secondary cycles can occur on corn
  • Heavy rain may wash spores away and destroy them
slide11

Sweet Corn Rust - Control Strategies

  • Resistant cultivars
  • Cultural practices
    • Rotation
    • Field preparation
  • Fungicides
    • Bravo - fresh market only
    • maneb
    • mancozeb
    • Tilt
      • 4 fl. oz/A when rust first appears
      • 7-14 day schedule, 14 day PHI
      • 4 spray maximum
smut of sweet corn key points
Pathogen: Ustilago maydis

Affects both field corn and sweet corn but more severe on sweet corn

All above ground parts of the corn plant are susceptible

Fungus can invade directly through cell walls, or through wounds

Fungal galls are edible in early stages of formation

When the fungus breaks through the membrane cover, spores are disseminated to new sites by wind and splashing rain

Overwinters as resistant spores in galls and plant debris on soil surface

Smut of Sweet Corn - Key Points
slide16
Resistant varieties

Avoid mechanical injury to the corn plant especially following a rain.

Maintain good fertility

Cut off and burn galls before they burst (for the home gardener).

Smut of Sweet Corn - Control Strategies

slide20
Pathogen: Exserohilum turcicum (Helminthosporium turcicum)

Symptoms:

Lesions are long (1-8 inches), elliptical in shape, grayish-green or tan

Severe infection can lead to death of the leaf

Ear infection does not occur, but lesions can be found on the husks.

Affects at least 22 plants in the grass family including corn, sorghum, Johnsongrass, Sudangrass

Disease favored by frequent rain, high RH, heavy dew and relatively low temperature

Disease is limited by warm, dry periods

Overwinters as soil-borne debris from infected plants or in dried leaves on standing plants

Northern Corn Leaf Blight - Key Points

slide21
Some resistant varieties are available

Currently registered fungicides are available for commercial production.

Northern Corn Leaf Blight -

Control Strategies

sweet corn disease resistance
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance1
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance2
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance3
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance4
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance5
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance6
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties

sweet corn disease resistance7
Sweet Corn Disease Resistance*

WI= recommended for WI gardens, MD= maize dwarf mosaic, NB= no. corn leaf blight, R=rust, SB= so. corn leaf blight, SM =smut, SW=Stewart’s wilt, BW=bacterial wilt, C=cold

* See UWEX Publication A3110 for current disease resistant varieties